Agilent Technologies 8453 Operator's Manual page 144

Theory of Operation
Spectrophotometer Data Acquisition (SDA) Board
SCI—Spectrograph Connector Interface Board
The PDA, which includes control electronics for readout of the individual
photodiodes, is mounted on the SCI (spectrograph connector interface)
board. Gain switching is used to optimize the signal level to the dynamic
range of the A/D converter on the SDA board. In addition, wavelength
calibration data from the manufacturing process are stored in the resident
EEPROM to provide both wavelength precision and accuracy.
PDA Signal Conditioning Electronics
Data is transferred from the photodiode array (PDA) through the
spectrograph connector interface (SCI) board to the PDA signal conditioning
electronics. The PDA signal conditioning electronics adjusts the signal levels
to provide an appropriate output signal.
A/D Converter
The output signal from the PDA signal conditioning electronics is directed to
the 16 bit /160 kHz A/D converter. Multiplexing is used to monitor the signal
from the PDA temperature sensor which is used for temperature
compensation.
PFP–PDA Front-End Processor
The PDA front end processor (PFP) utilizing an on board RAM and the EPLD
(electronically programmable logic device) forwards the data from the 16 bit
A/D converter to the SPM board. It provides timing and control for the
photodiode readout and the A/D conversion.
Low-Pass Filter
Signals between the SPM board and the switches and LED on the
spectrophotometer sipper interface (SSI) board are routed through a
low-pass filter for RFI (radiated frequency interference) improvement.
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